This invention relates to an improved process for the production of tolyltriazole in which the tolyltriazole is a lighter colored product. The color improvement in the tolyltriazole produced from this process occurs when the ortho-toluenediamine reactant is previously stabilized by treatment with a compound selected from the group consisting of aldehydes, ketones, acetals and ketals. The process of the present invention reduces the need to filter (or distill) the tolyltriazole prior to being used commercially.
Processes for the production of tolyltriazoles and benzotriazoles are known and described in, for example, U.S. Pat. Nos. 2,861,076, 3,227,726, 3,564,001, 3,637,514, 3,639,431, 3,732,239, 3,970,667, 4,158,660, 4,363,914, 4,424,360, 4,439,361, 4,528,381, 4,549,026 and 4,918,195, and GB Patent 1,581,407. Solid tolyltriazoles are formed in some of these processes and liquid tolyltriazoles are formed in others.
Tolyltriazoles are known to be useful as corrosion inhibitors, particularly for copper surfaces, synthetic detergents and antifreezes, as UV stabilizers, as intermediates in numerous syntheses such as, for example, dyes, and in water treatment applications. Typically, however, for these tolyltriazoles to be suitable for certain applications, it is necessary for the tolyltriazole to be of considerably high purity. Discoloration inherently occurs during the processes for producing tolyltriazole due to chemical oxidation of compounds such as, for example, ortho-toluenediamine. Therefore, it is usually necessary to purify tolyltriazoles.
Suitable processes known for purifying tolyltriazoles and benzotriazoles are known and described in, for example, U.S. Pat. Nos. 3,732,239, 3,970,667, 4,528,381 and 4,918,195, and in GB Patent 1,581,407. When crude diaminotoluene is used as the reactant before starting diazotization and ring closure reaction, U.S. Pat. No. 3,732,239 discloses that it is necessary to subject the produced tolyltriazoles to an expensive purification via distillation. As described in U.S. Pat. No. 3,970,667, the reaction mixture containing triazole (with no intermediate isolation of tolyltriazole) can be made alkaline using aqueous sodium hydroxide solution and being subjected to several clarifying filtrations, and once the mixture is made again acidified via nitric acid, the precipitated triazole can be isolated. GB Patent 1,581,407 discloses that once volatile components are distilled off the reaction mixture, the mixture is inoculated and the triazole is recovered by crystallization.
It has also been attempted, following the diazotization with sodium nitrate in a water/acetic acid reaction medium, to first separate off the benzotriazole as an oil, wash it with water, and to distill the benzotriazole under reduced pressure. This simple vacuum distillation was not completely satisfactory though, as U.S. Pat. No. 4,170,521 discloses the vacuum distillation of benzotriazole in the presence of a small amount of formaldehyde.
U.S. Pat. No. 4,528,381 further discloses that these distillations did not provide fused triazoles of sufficient purity and color stability. It is described in this reference that to avoid unsatisfactory distillation, the fused triazoles are reacted with alkyl nitrites in the presence of alkanols (C.sub.6 to C.sub.10 alkanols) as the reaction medium. The resultant triazole is then extracted from this reaction medium by means of aqueous sodium hydroxide solution.
Although progress has been made in the area of purifying tolyltriazoles, the need for additional improvements still exists. Methods to purify tolyltriazoles which are easier, less time consuming and/or more economical than those currently known and presently being used are of interest and important in this field of chemistry.
It has now been found that a high purity tolyltriazole can be readily produced by conventional diazotization processes of ortho-toluenediamine with a nitrite, if the ortho-toluenediamine has first been stabilized against discoloration by the addition of a small quantity of certain types of compounds. This process reduces or possibly eliminates the need for the prepared tolyltriazoles to be further purified prior to being used.
Advantages of the present invention include the fact that it is not necessary to modify the existing tolyltriazole process equipment to install purification steps. The tolyltriazole produced by the present invention will require less decolorization. Also, since this invention modifies the raw material (i.e., o-TDA) used as a reactant in the process and not the actual tolyltriazole process, this results in a substantial cost savings due to decreased processing requirements.